7. CONCLUSIONS

Some of the hot meals exceeded the microbiological standards accepted
by the AEA for
E. coli
(8.2%),
S. aureus
(0.6%),
B. cereus
(0.7%) and for
C. perfringens
(0.7%). Total counts higher than 10
6
cfu/g, which
is the AEA limit for food items that have been handled after heat treatment,
were found in 9.2% of hot meal samples. Total counts above this limit indicates
shortcomings in food preparing practice. Although the frequency of food
poisoning bacteria was rather low, their occurrence may indicate a risk
of food poisoning via hot aircraft meals. However, hot meals undergo final
re-heating on board, which decreases the microbial count of hot meals and
thus the risk of food poisoning. There were significant differences between
preparing countries regarding the microbiological quality of hot meals
reflecting
the level of production hygiene.

Many of the cold meals failed to meet the AEA standard for
E.
coli
(14%),
S. aureus
(7%) and for
B.
cereus
(3%). The contamination rate in respect of these bacteria
was higher in cold meals than in hot meals. Such a high level as the 10
6
cfu/g for
E. coli
found indicated poor microbiological
quality of meals. The maximum levels of
S. aureus
and
B. cereus
found, 10
3
cfu/g and
10
4
cfu/g, respectively, mean
shortcomings in microbiological quality and indicate a risk of food poisoning.
In the case of cold meals, the level of hygiene of the preparing country
seemed to reflect to the microbiological quality of the meals, too. Stricter
control measures should be focused particularly on the production of cold
aircraft meals, which seemed to be even riskier than the hot ones.

The prevalence of
Salmonella
was low in cold
meals (0.1%), but the only positive finding detected was connected with
an outbreak among air passengers. The prevalence of
Salmonella
in hot meals was higher (0.3%). However, none of them were reported to be
connected with outbreaks. If final re-heating on board is properly carried
out, it should destroy
Salmonella
contamination. This
means a higher risk of
Salmonella
associated with cold
served dishes than with hot served ones.

Nintyone airline passengers and 107 railway passengers became infected
with
S
. Infantis via food prepared in a flight kitchen. A
high number of the flight catering employees 28/162 (17%), also became
infected via breakfast prepared in the flight kitchen and served in their
canteen. This figure included many 23/118 (19%) of the catering establishment’s
food handlers. It was impossible to establish the origin of this
Salmonella
outbreak. The employees’ breakfast had probably been contaminated by a
symptom-free
S.
Infantis carrier in the flight kitchen.
Many of the food handlers became infected and this subsequently led to
widespread contamination of food products of the flight kitchen. Air passengers
became infected via contaminated meals served on a charter flight and
railway passengers via contaminated egg sandwiches served on several train
routes.
S
. Infantis was isolated from one hot meal
sample representing the batch served on the particular charter flight.
The most prominent contributing factors were found to be that food handlers
suffering from mild diarrhoea were not excluded from work and that there
was no hygiene education or supervision for food handlers. A heat wave
combined with a shortage of refrigeration facilities and possible malfunction
of the re-heating oven on board were regarded as contributing factors,
too. The results of the investigation showed that preparing meals for
aircraft is a high-risk operation, which calls for strict hygiene requirements
and a thorough knowledge of food hygiene.

Hand and nasal sampling showed a substantial prevalence, 6% and 12%
respectively,
of the carriage of enterotoxic
S. aureus
among flight catering
food handlers. Nasal carriers can easily transmit
S. aureus
into the hands and this means a potential risk of food poisoning. Because
S. aureus
colonises primarily in the human nose, nasal
sampling is a better way of detecting
S. aureus
carriers
than hand sampling. Testing food handlers working in high-risk premises
such as in flight catering provides valuable information about carriers.
It helps in planning preventive measures, such as special hygiene instructions
for carriers to avoid contamination of food. Characterisation of isolated
strains by pulsed-field gel electrophoresis is very useful especially
by tracing the contamination source. It also revealed that more than one
clone can be harboured by one employee.